My invention shows a driving aid useful in a motor vehicle having an automatic transmission coupled between the engine and the wheels of the vehicle. With the advent of ever increasing energy costs for gasoline, diesel fuel and other portable organic fuels, much concern centers on improving the attainable fuel milage from the automobile, truck, and other vehicles. In particular the highway milage and commuting milage of such vehicles has been given much attention in recent times. This is conveyed even more forcefully by government mandated deadlines on overall improvement in "fleet" fuel milage which must be met by every manufacturer of automobiles, and eventually by most other motor vehicles.
The use of a standard manual shift transmission in lieu of an automatic does afford an improvement in milage, but the basic inconvenience of the manual shifting and the use of the clutch makes the automatic transmission far more preferable by a large segment of the driving population, even at the sacrifice of additional operating cost. My invention now addresses the urgency of aiding the driver of an automatic transmission equipped vehicle to attain overall economy of operation approaching that of a manual shift transmission.
In the conventional automobile and truck which includes an automatic transmission, the usual automatic transmission further includes a torque converter component. The automobile type internal combustion engine, whether gasoline or diesel powered, can normally be expected to operate at near peak efficiency, and therefore with best fuel milage economy, when it is delivering about a constant torque into its load. Since the automatic transmission is already fitted with a torque converter, a measurement of the delivered absolute torque can be derived by computing the slip through the torque converter. The slip is the difference in the instant converter output member rotational rate relative to the input member rotational rate and is largely proportional to the absolute torque demand coupled through the converter at higher vehicle speeds. This slip may be conveniently measured by deriving the difference between the engine r.p.m. speed and the effective torque converter output member rotation rate. In the conventional construction of a unitized automatic transmission and torque converter, the torque converter is mounted directly onto the input shaft of the gearbox portion of the automatic transmission. This makes direct access to the rotating output member of the torque converter inconvenient. The output shaft from the transmission gearbox usually couples to the vehicle driveshaft and to the differential and wheels of the vehicle. When the gearbox effective output driveshaft rotation rate is measured and compared with the engine output member r.p.m. speed, and the mechanical gear ratio obtained through the transmission gearbox is allowed for, the absolute slip through the torque converter is provided as derived information. Through the expedient of computing the converter slip, which reflects relative torque and which furthermore can be adapted to allow for different values of normal slip through the transmission which may be proportionally related to the instantaneous speed and other factors such as transmission temperature, a very accurate indication can be provided to the driver or operator of the vehicle as to when he is driving in such a manner as to enhance his fuel economy.
A constant torque measuring system, such as this novel driving aid provides, teaches uniform driving habits and goes beyond merely saving fuel and thereby saving the vehicle operator much money. It also acts to reduce the strain on the mechanical components of the vehicle. In particular the clutches in the automatic transmission see less abuse. The tires on the vehicle also see a relatively constant torque demand and thereby tire wear due to slippage with the drive surface may be somewhat reduced.
A driver adjustable "PERFORMANCE SELECTOR" affords an entirely new dimension of a driving aid's ability to meet the driving habit demands of an individual driver, allowing for several degrees of economical driving performance as traded off with acceleration and speed of the vehicle. This novel ability to tune the driving aid to the drivers habits is believed to make the applicability of the invention far more universal, acceptable by a broad spectrum of the driving population.
In so far as is known to me, no other device provides a driver with a real-time, on-road indication of the relative constancy of torque delivery by the engine to the load. Moreover, no prior system is known which effectively measures the engine r.p.m. thereby producing a signal which combines with a signal produced by measuring the automatic transmission torque converter output shaft rotation rate to provide a computed signal proportional to the apparent torque being delivered by the engine to the load. Additional novelty of the invention includes the combining of engine or transmission temperature and engine manifold vacuum pressure to modify the derived indication in order to correct for slip relatable factors affecting the accuracy of the computed torque signal and to skew the indication favorably to maximize not only the vehicle's fuel performance, but also its acceleration and other driving characteristics.